There are many chemical processes where solid particulate matter, such as catalyst, and a hydrocarbon gas are contacted. Frequently, chemical reactions and physical phenomena occur for a predetermined period of time in a reaction zone, contained in, e.g., a moving or fixed bed reactor. Often, the gas/solid contacting is in a continuous or semi-continuous manner instead of a batch operation. In such an instance, catalyst particles may be introduced and withdrawn from the reactor, which can be at a higher pressure than the source of the catalyst particles, such as a regenerator.
Hydrocarbon conversion units can include a reactor with one or more moving bed reaction zones used in conjunction with a regenerator. The reactor can include several reactor zones and can be structured in the form of a stack, or be split into sections to reduce the overall height. Typically, the regenerator with an atmosphere containing oxygen operates at a lower pressure than the reactor with an atmosphere containing hydrogen. Once the catalyst is transferred from the lower pressure to the higher pressure, a lift may be used to transfer the regenerated catalyst to the reactor. After the catalyst is spent, another lift can be utilized to transfer the catalyst from the reactor to the regenerator. Generally, the separation of the atmospheres of the reactor and regenerator is wanted to prevent undesirable side reactions.
Introducing catalyst particles into a high-pressure reactor from a regenerator can pose difficulties. Equipment, such as screw conveyors or star valves, can degrade solid catalyst into smaller particles, which in turn may create wear and tear on processing equipment. Another option may be a transfer vessel having double block-and-bleed ball valves to control the entry of regenerated catalyst into and out of the vessel. The catalyst entering the vessel can be purged with nitrogen to remove oxygen and pressured with hydrogen up to the reactor pressure before transfer into the reactor. After catalyst exits the vessel, the vessel can be purged with nitrogen to remove the hydrogen before filling again with catalyst. Such a transfer vessel can separate the hydrogen atmosphere of the reactor from the oxygen atmosphere of the regenerator. However, this vessel can require that the block-and-bleed ball valves be maintained in excellent working condition. A leak in either of the block-and-bleed ball valves may result in gas leakage impeding the transfer of the catalyst through the transfer vessel.
Another transfer vessel can be a valveless lock hopper that can include three sections. Generally, catalyst is received in a top section where it is intermittently transferred to a middle section. The middle section can allow catalyst to flow in before being transferred to the bottom section. A standpipe's diameter may be sized in the middle section so that gas flowing upwards can stop catalyst flow while allowing catalyst flow through another section of the pipe. This may be achieved by the alternate opening and closing of equalizing valves positioned on a pipe communicating with all three sections and in a parallel relationship with the catalyst flow. As an example, when the equalizing valve between the top and middle section is open, the valve between the middle and bottom section is closed so gas flowing up the lower standpipe will prevent catalyst flow from the middle zone through the lower standpipe yet allow catalyst flow into the middle zone through the upper standpipe. Repeated cycling of the equalizing valves will allow a controlled flow of catalyst from the low pressure of the regenerator to the high pressure of the reactor.
However, it may be desirable to reduce the height of a hydrocarbon conversion unit to reduce the cost of construction and maintenance. Particularly, tall structures can require additional expense in fortifying the foundations to withstand the high heights of construction, and subsequent impact of harsh weather events. Moreover, once these units are constructed, they can exceed 60 to 90 meters (200 to 300 feet) in height and incur greater maintenance costs compared to units of lesser height.
Often, a regenerator is built in parallel to the reactor. The regenerator can include other vessels, such as an elutriation vessel and a valveless lock hopper. Even if the reactor stacks are split to reduce their height, the regenerator is typically a single vessel and can still have a substantial height to provide sufficient capacity to regenerate the catalyst used in one or more of the reactors. Moreover, often other vessels, such as the elutriation and transfer vessels, are stacked with the regenerator. As such, the overall height of the three vessels can be quite substantial, even if the reactors are split.
When the differential pressure between the regenerator and the reactor is large, generally the standpipes in the valveless lock hopper are longer. The longer standpipes can increase the overall height of the valveless lock hopper, and thus, the entire unit. In such an instance, it would be desirable to reduce the overall regeneration structure height, particularly in cases where the reactor is split into sections. It would also be desirable to reduce the height of the regeneration structure to be that of the reactor. Moreover, sometimes operating at a greater pressure differential between a regenerator base and lift is desired to provide more tolerance for process upsets. However, operating at a greater pressure differential can result in longer lines, and hence may further increase the height of a unit.
Consequently, there is desire to reduce the overall height of a hydrocarbon conversion unit, particularly the regeneration structure. Moreover, there is desire to utilize a transfer apparatus that has a lesser elevation compared to other transfer apparatuses.